In a wireless communications system such as, for example, a system of the LTE (Long Term Evolution) kind, there will be one or more controlling nodes, so called base stations, sometimes referred to as eNodeB, depending on the specific kind of system. One role for a base station is to control all traffic to and from user terminals within a certain geographic area in the system, a so called cell.
A base station in a cellular system will comprise one or more transmitters, each of which in turn comprises one or more power amplifiers, PAs. The PAs are one of the main consumers of energy in a base station, since the PAs are used to amplify input signals with low input power to output signals with high output power, which is due to the fact that a high output power level is required to provide adequate coverage and high data rates in a cellular network.
A PA in an average base station has an output power of approximately 20 W and an efficiency level of around 20%, which means that approximately 100 W are needed in order to obtain a PA with an output power of 20 W. Reducing these power levels would thus mean major savings in energy, and would also lead to further savings in energy due to, inter alia, reduced cooling needs.
In many cellular systems, both those comprising an FDD (Frequency Division Duplex) mode and those comprising a TDD (Time Division Duplex) mode, the base stations transmit in so called radio frames, each of which will comprise a number of sub-frames.
As can be understood from the explanation given above, a reduction in the energy consumed by a PA in a wireless communications system would be highly beneficial, both in order to reduce operator expenditure (OPEX) and for environmental reasons. One way of achieving this would be to reduce the number of sub frames in which transmission is made from the base station, or to reduce the transmission in certain sub frames. or entirely “shut down”.